The objective of this research program is to understand, on the molecular level, the mechanism of avian proviral DNA synthesis and its integration into host cell DNA. Currently, we are investigating the role of the individual subunits of the avian reverse transcriptase in proviral DNA synthesis, which includes the action of ribonuclease H on in vitro DNA synthesis. A newly identified virus-coded polypeptide has been identified in AMV and Rous sarcoma virus. The biological role is presently under investigation.